The present application is directed to additive manufacturing processes for the production of electronic devices and/or components, and more particularly to manufacturing low cost display backplanes implementing TFT arrays configured using additive printing techniques.
Additive printing, additive processing and other similar terminology refer to processes were material is configured into electronic devices and/or components without the need of subsequent steps to remove portions of the material. This is in contrast to typical subtraction fabrication techniques which deposit, lay down or otherwise provide material, followed by removal of selected portions of the material.
Therefore, additive processing, including additive printing, has the potential for reducing the amount of material wasted in a manufacturing operation, as well as minimizing the number processing steps needed complete a manufacturing process, compared to traditional subtractive processing.
In additive printing each material can be deposited where it needs to be in a single process step, and the only wasted material is solvent. Additive printing requires solution-based materials and printing processes and devices capable of printing with the necessary precision. Two examples of devices which have been constructed by the use of additive printing in the display technology area are PLED displays and LCD color filters. A review of using additive printing for the formation of TFTs as well as other active components is set forth in R. A. Street et al., “Jet Printing Flexible Displays”, Materials Today, Vol. 9, Issue 4, April 2006, pp. 32-37. A discussion regarding methods used to deposit and integrate solution-processed material to fabricate TFT backplanes by inkjet printing are also discussed in the article by Ana C. Arias et al., “All-Additive Ink-Jet-Printed Display Backplanes: Materials, Development and Integration”, Journal of SID, Jul. 15, 2007, pp. 485-489. Still further, a specific method of producing electrical circuit elements to control electronic displays using additive methods is described in U.S. Pat. No. 6,521,489, titled, Preferred Methods for Producing Electrical Circuit Elements Used to Control an Electronic Display, to Duthaler et al., issued Feb. 18, 2003.
Thus, research directed to low-cost display backplane fabrication which employs additive printing for some or all of the layers that make up a TFT circuit is ongoing. A particular candidate material for use in additive printing processes is nano-particle silver, which can be readily printed and sinters at low temperature to form a highly conductive film. One discussion regarding such nano-particles is found in U.S. Pat. No. 7,270,694, titled, Stabilized Silver Nano-Particles and their use, to Li et al., issued Sep. 18, 2007. The '692 patent includes a process where a plurality of silver-containing nano-particles with molecules of a stabilizer are on the surface of the silver-containing nano-particles. The resultant solution is noted to be of particular benefit in the use of various applications, including production of thin film transistors (TFTs), light emitting diodes (LEDs), RFID tags, photovoltaic cells, among others.
As mentioned, a desirable aspect of additive printing is that it minimizes the processing steps needed to manufacture electronic components. Additive printing also reduces the material which is wasted resulting in lower material cost. Therefore, the conventional thought is to focus on improving additive printing processes to lower the number of manufacturing steps. However, it is also appreciated that for certain steps the materials needed to achieve the printing operations are themselves quite costly. For example, the mentioned nano-particle silver as well as other high-cost metal and/or non-metal solutions are extremely expensive, which adds undesirable costs to the manufactured electronic device and/or component. Therefore, to improve the overall effectiveness of the additive processes it is desirable to address the issue of high-cost metal and/or non-metal solutions.